MIT辐射实验室丛书：V3-雷达信标技术解析

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"MIT辐射实验室丛书 V3-RADAR BEACONS" 本书是《雷达系统工程》丛书中的一卷，该系列由美国麻省理工学院辐射实验室的专家在二战后共同编撰，旨在分享他们在雷达技术开发中的经验与知识，由麦克劳希尔出版社于1947年发行。在"PART I BASIC CONSIDERATIONS"部分，作者探讨了雷达信标的基础概念和应用。"CHAPTER 1 THE USES OF BEACONS"由L.A. Tubner和A. Roberts撰写，详细阐述了雷达信标的作用和原理。 1.1章节首先介绍了雷达信标的基本性质。雷达系统通过发射强大的无线电波脉冲，然后接收返回的回波来工作。回波与发射脉冲之间的时间差可以计算出目标的距离。通过适当的天线系统，雷达能将无线电能量聚焦成狭窄的波束，类似于聚光灯聚焦光线。这样，只有当雷达设备对准目标时，才会接收到回波。通过控制天线的运动和阴极射线管的强度调制电子束的扫描，可以在显示器上为操作员描绘出目标区域的平面视图。然而，对于某些情况，简单的雷达装置可能不足以应对。例如，当小型飞机处于远距离时，其回波可能过于微弱，无法被观察到。这就是引入雷达信标的原因之一。雷达信标是一种主动式雷达系统，它定期发射特定的信号，使得即使在弱信号环境下，也能被雷达设备检测到。它们常用于导航、航空、海洋和气象监测等领域，帮助定位和跟踪远程或小型目标。信标系统的工作方式通常包括发射预设频率和模式的信号，这些信号在雷达显示器上产生可识别的特征，从而帮助区分不同的信标或排除干扰。信标的种类多样，包括连续波信标、脉冲信标和编码信标等，每种都有其独特的应用场景和优势。在实际应用中，雷达信标与雷达系统的结合使用极大地提高了探测的准确性和可靠性。例如，在航海中，船舶可以利用陆基的雷达信标确定位置，避免危险的水域；在航空中，飞行员可以依赖地面的雷达信标进行精确的进近和着陆。此外，雷达信标还在自动导航、交通管理、搜索与救援等任务中发挥着关键作用。《MIT辐射实验室丛书 V3-RADAR BEACONS》深入浅出地讲解了雷达信标的核心原理及其在各种情境下的应用，为读者提供了宝贵的雷达技术理论与实践经验。

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THE USES OF BEACONS [SEC.1.10

A solution for many of the difficulties encountered in the Oboe system

is to be found in its converse, which is called the “H-system.”

In an

H-system, the aircraft carries an interrogator and measures precise

ranges to two ground beaconsat accurately known locations.

(See Fig.

1.10.)

Courses Possible. -In an H-system, the crew of the aircraft has

control of the courses to be flown.

With suitable instrumentation, a

variety of choice is possible. Cat-mouse courses maybe flown, as in Oboe.

In addition, courses such that the difference of range to the two ground

beacons is constant may readily be flown; such a course is a hyperbola.

Mousebeacon

England

London

The H-system

FIG.I.IO.—TheH-system. This ie the converseof

aircraftcarriesaninterrogator,andthetwo groundstationsarebeacons.

~ O.sseldorf

Miles

L_+!!

the Oboesystem(Fig. 1.10). The

With a suitable computer and instrumentation, arbitrary courses may

be flown. Such computers were designed but not used in combat.

Comparison of Oboe and H-systems.-The major advantages of an H-

system over an Oboe system are the following:

A very large number of aircraft can use the system at one time;

in Oboe, one airplane is directed at a time by one pair of ground

stations. 1

Each plane can, if desired, attack a different target; many more

targets are thus possible than with Oboe.

No communication to aircraft from ground stations, or between

ground stations, is required; much less organizational effort is thus

required to set up a mission.

I More complex Obos zyatemswhich permittedsimultaneouscontrol of several

plawa weredesignedbut not put into operation.

SEC.1.10]

H-SYSTEMS

4. As noted above, a wider variety of choice of course to be flown

is possible.

5. In the case of aircraft carrying bombing radars, little auxiliary

equipment is required for beacon interrogation; the same aircraft,

therefore, can be used for either radar or H-bombing. Oboe

requires more specialized aircraft.

Several different H-systems were used in the war. We will examine

these briefly.

“Gee-H.’ ‘—This British system was made by altering ground stations

of the Gee hyperbolic navigation system so that they operated as beacons.

Additional equipment was added to the aircraft Gee receiver to convert

it into a Gee-H beacon interrogator.

Both the RAF and the Eighth Air

Force used this system successfully during the last year of the war in

Europe.

Rebecca-H.—By altering the airborne Rebecca indicator, provision

was made for displaying two beacon responses simultaneously on an

expanded delayed sweep.

The standard Eureka beacons were used.

Installed in photo-reconnaissance aircraft of the RAF, Rebecca-H was

used to direct airplanes to locations at which reconnaissance photographs

were required.

Micro-H.—The 3-cm bombing radars AN/APS-15 and AN/APQ-13

were designed with beacon interrogation provisions and with expanded

delayed sweeps. They were thus readily adaptable to H-bombing. The

Eighth Air Force used the AN/APS-15 (called “Mickey” by the crews)

together with 3-cm beacons (sometimes called “Minnie”) for H-bombing

during the last nine months of the European war. This system was

known more formally as Micro-H.

Micro-H and Gee-H helped turn

the tide toward victory in the battle of the Ardennes (the ‘(Bulge “).

Shoran.—Probably the first of all H-bombing systems to be designed,

Shoran was also the best instrumented and the most precise. It was,

however, the last to be produced and used. It consisted of an interroga-

tor-responsor and beacons especially and solely designed for H-bombing.

It was used with remarkable success by the Fifteenth Air Force in Italy

and the Ninth Air Force in Germany, and was nearly ready for use

against Japan when the war ended.

HOW BEACONS ARB USED

We have reviewed briefly the major uses to which beacons were put

during the war. Because beacons boast no peacetime history, an analy-

sis of their wartime uses is the best guide to how they may be used in the

future. Such an analysis may be made from at least two points of view.

We can analyze beacon systems according to the functions they perform

18 THE USES OF BEACONS [SEC.1.11

or according to the functions that need to be performed. A brief analy-

sis from each of these points of view is given below.

THE FUNCTIONSOF BEACONS

The data obtained from beacon replies differ somewhat from those

obtained from a radar echo. Replies from beacons, foronething, convey

more information.

In the case of radar echo, the information obtained is entirely depend-

ent upon the characteristics of the radar set and target. The range of

the echo is measured with a precision characteristic of the timing circuits

of the radar set. The azimuth is measured with a precision characteristic

of the azimuth-determining equipment of the radar. Resolution in

range depends upon the pulse duration; and resolution in azimuth depends

on the antenna characteristics and the frequency used.

The beacon reply may be treated like an echo by the interrogator,

as faras range and azimuth determination are concerned. If the beacon

reply is coded, however, it conveys information about the beacon. It

may tell, for example, where the beacon is; in this case coordinate infor-

mationis transmitted. It may identify itself by conveying identifying

information. Finally, if the beacon system is properly designed and

used, it may communicate still other general information.

1.11. Coordinate Fixing.-Beacons can be used to mark and identify

known positions on the ground so that an airplane can determine its

position with reference to them. The combination of an airborne

interrogator with ground-based beacons thus constitutes an additional

aid to navigation, which is compared with other types in Sees. 1.18 to 1.22.

When a fix of ordy moderate accuracy (within about a mile or two)

is needed, the determination of the range and bearing of one beacon

suflices. Fortheutmost accuracy-determinationof position to within

100 ft-distances to two beacons at known positions are measured

simultaneously because range can readily be measured much more

accurately than bearing. Systems of this latter type are useful in

applications demanding great accuracy. These include bombing,

mapping by airplane photography, in which high accuracy of fix of the

camera is required, and similar applications. It is necessary, of course,

that the beacon delay—the brief time required for it to reply—be made

constant and that allowance be made for it.

Obviously, the converse application can be made. The location of a

beacon-carrying aircraft can be determined accurately by one or more

ground stations at known positions. As we have seen, some systems of

precision bombmg employed in the war used beacons in this way. In

principle, the beacon was superfluous because the radar echoes of the

aircraft might have sufficed. In practice, however, the beacons ensured

SEC. 1.12] IDENTIFICATION

reliable operation at long range and positive identification of the aircraft.

Shore beacons may be used with shipborne interrogators as lighthouses

are used. Observation of a single beacon determines a fix. The ship

gets not only the bearing, as it does from a lighthouse, but also the

range.

Shipborne interrogator-shore beacon systems should be especially

useful under conditions of poor visibility. Beacons have not been widely

used in this way so far, but the introduction of such a system is now

contemplated by the U.S. Coast Guard.

The coordinates of the interrogator may be determined whenever a

beacon is located at a known position and a fix is taken on it, and the

coordinates of a beacon may be determined when a fix is taken on it by a

stationary interrogator of known position.

When neither the interrogator nor the beacon is at a known location,

relative coordinates are still of value for homing. ,Thus, a naval aircraft

may home on an aircraft carrier without knowing its precise location

and, indeed, while its location is changing. Similarly, aircraft may home

on a ground beacon without caring where it is, as in Rebecca-Eureka.

Since a series of fixes determines a course, it is possible to set a course

and navigate it by means of beacons.

It is easy to remain within a mile

of such a predetermined course, and even within a quarter of a mile

without too much trouble. Greater precision requires some special

instrumentation, such as an expanded sweep; with the aid of such

instrumentation, however, a ship or airplane can remain within 100 ft of a

predetermined course. By such methods, it is feasible to fly an aircraft

by instruments to an airport, to let down through an overcast, and to

emerge from it at an altitude of 100 ft, directly over the end of the

runway.

1.12. Identification.-An airplane or ship equipped with a beacon of

particular characteristics is thereby marked and identified to some extent,

as we saw in previous discussion of IFF, the identification system used

most widely during the war. Because aircraft were often detected by

radar long before they could be seen, the problem was one of classifying .

the radar-reply pips as belonging either to friendly or to hostile aircraft.

The radar sets were of many different types, operating over a wide range

of frequencies; each one, therefore, had to be provided with a separate

IFF interrogator-responsor working at one of the frequencies chosen for

the IFF system. The interrogator was often synchronized with the

radar set so that the interrogating pulses went out together, and the

radar echoes and IFF replies arrived together and could be displayed on

the same indicator tube to give proper correlation in range. In order to

hinder the enemy in using captured transponders for deception, IFF

beacons were coded in various ways.

A thorough presentation of the

special problems of IFF would require another volume.

They will not

THE USES OF BEACONS

[SEC. 113

be treated further in this book, partly because many of them do not arise

in peacetime uses of radar or beacons, and partly because IFF has been

considered, oddly enough, as particularly sacred from the standpoint of

military security.

There is a peacetime problem of identification, however, that is

closely related to that of IFF. It is the problem of identifying any

particular one of many radar echoes in the neighborhood of busy airports

when airplane traffic is being controlled through radar surveillance.

A beacon with enough complication of coding to give positive individual

identification of every aircraft seems to be needed. Fortunately, the

problem is simpler than the IFF problem in one respect: It is not necessary

that all aircraft have their identifying beacons turned on at nearly all

times.

The identifying reply codes of fixed navigational beacons are assigned

by a central authority and published for the information of those who

use them. An aircraft navigator within range of such a beacon identifies

the beacon by means of its code, and thus can locate the aircraft with

respect to the beacon. The code of a shipboard beacon identifies the

ship carrying it.

1.13. Communication.-By its very nature the beacon system

involves the use of two nearly independent send-receive systems, as do

all two-way communication systems.

Furthermore, it is rather wasteful

of its portion of the electromagnetic spectrum in that the r-f bandwidth

required for satisfactory transmission of the simple pulses would permit

the superposition of intelligence-conveying modulation. The various

kinds of reply codes mentioned in Sec. 1.2 can be considered as commu-

nication of a rudimentary sort.

So can interrogation codes that ensure

that the beacons will reply only when properly interrogated. Coding of

both kinds and several more elaborate ways of using the beacon channels

for communication and remote control are discussed at length in succeed-

ing chapters (Chaps. 5 and 11).

TYPES OF BEACON SYSTEMS

1.14. Air-to-surface Systems.—A method of classification of radar-

beacon systems that brings out some points of interest is according to the

location of the interrogator and of the beacon. Thus, an air-to-surface

system is one in which an airborne interrogator works with a beacon

located on the surface of the earth.

The beacon in such a system may be used as a reference point for air

navigation, as we have already seen. If so, it usually has a receiver of

good sensitivity and a powerful transmitter so that it may be interrogated

and received by all aircraft out to horizon range. Beacons of this kind

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